Method for preparing tris (alkylamino) boranes



United States Patent 3,139,453 METHOD FOR PREPARING TRIS(ALKYLAMINO) EQRANES Howard Steinberg, Fullerton, and Allen L. McCloskey, Orange, Calif., assignors to United States Borax & Chemical Corporation, Los Angeles, Calif., a corporation of Nevada No Drawing. Filed Nov. 26, 1958, Ser. No. 776,410 Claims. (Cl. 260-551) This invention relates as indicated to a method for the preparation of tris(alkylamino)boranes. The products of the present process will be found to have utility as fuel additives.

It is therefore the principal object of this invention to provide a new method for producing tris(alkylamino)- boranes.

Other objects will appear as the description proceeds.

To the accomplishment of the foregoing and related end, said invention then comprises the features hereinafter fully described and particularly pointed out in the claims, the following description setting forth in detail certain illustrative embodiments of the invention, these being indicative, however, of but a few of the various ways in which the principle of the invention may be employed.

Broadly stated, the present invention comprises the method of producing tris(alkylamino)boranes which comprises reacting one mol of a boric acid ester having an alkyl group of from 1 to 5 carbon atoms with at least three moles of a material selected from the group consisting of primary aliphatic amines having an alkyl group of at least 4 carbon atoms, cyclohexylamine, cyclopentylamine, and tetrahydronaphthylamine, and isolating tris- (alkylarnino) borane from the reaction mass.

It will be seen in the foregoing broadly stated paragraph that at least three moles of the amine are necessary to react with the borate ester to form the tris(alkylamino)- borane. No upper limit has been set on the amount of amine used since it is only important that at least three moles are present. However, from a practical standpoint it would be economically undesirable to use amine in great excess, and in the preferred embodiment of our invention we use about 3.5 to about 5 moles of amine. As for the primary aliphatic amines it will be noted that an amine having an alkyl group of at least four carbon atoms is necessary to the present reaction. It is the full intention of the present invention to include any primary aliphatic amine having an alkyl group containing four or more carbon atoms. However, here again economics plays its parts and in the preferred embodiment of the invention we use amines with an alkyl group having from 4-12 carbon atoms.

It is also important to note here that in order to produce a tris(alkylan1ino)borane from the above-mentioned ingredients it is necessary to maintain a stoichiometry wherein at least three moles of amine are reacted with one mole of the borate ester. This critical stoichiometry is based on the boron utilized in the reaction. Those skilled in the art will readily recognize that in the cases where methyl and ethyl borates are used these materials always form azeotropes in the presence of their alcohols. It is also well known to those skilled in the art that in the case where methyl borate is used it becomes necessary to use four moles of the methyl borate ester instead of the one mole described in the foregoing broadly stated paragraph, because three moles of the ester distill as the esteralcohol azeotrope, which has a lower boiling point than any of the other ingredients, and thus is carried out of the system leaving behind one mole of the methyl borate ester which reacts with the amine present. Thus it now becomes obvious that while it is necessary to use four moles of methyl borate ester, in all actuality only one mole of the methyl borate ester is reacted with the amine, and thus the foregoing critical stoichiometry is preserved. In the case of the ethyl borate ester, again the formation of the azeotrope must be taken into account in determining the amount of borate ester needed to furnish the one mole of ester which is to react with the correct amount of the amine. Again those skilled in the art know that it is necessary to use 1.48 moles of ethyl borate in order to have one mole of ethyl borate present to react with the amine. As for the higher borate esters, of course it is unnecessary to be concerned about the amount of ester used since borate esters having alkyl groups of three or more carbon atoms do not form azeotropes with their alcohols, and thus it is only necessary to utilize the required one mole of ester.

The following examples are given to illustrate the present process:

Methyl borate, 104 grams, was added to 58 grams of n-butylamine in a flask. This corresponds to an equivalent mole ratio of one mole of utilizable borate ester to 3 moles of the amine. The methyl borate azeotrope distilled at B.P. 5456 C. through a 24-inch fractionating column. Excess amine was distilled and the resultant tris (n-butylarnino)borane distilled at B.P. IDS-106 C./l

isopropyl borate, 94.0 grams, was added to 200 grams of cyclohexylamine. These amounts of ingredients are equivalent to a stoichiometry of one mole of isopropyl borate and four moles of cyclohexylamine. The isopropyl alcohol distilled through a 24-inch fractionating column. Unreacted amine and ester were distilled, leaving a residue which was heated to C. to remove the last traces of alcohol. This residue had the composition of tris(cyclohexylamino)borane.

III

A mixture of 300 grams (3.5 moles) of cyclopentylamine and 188 grams (one mole) of isopropyl borate Was heated at reflux and the alcohol produced was fractionated through a 24-inch fractionating column. After all the alcohol and excess amine had been distilled the resultant residue comprised tris(cyclopentylamino)borane.

A mixture of 147 grams (one mole) of 1,2,3,4-tetrahydro-Z-naphthylamine and 58 grams (0.25 mole) of n-butyl borate was heated under reflux and the n-butyl alcohol was fractionated through a 24-inch column. Excess amine was distilled at reduced pressure. The resultant residue was tris(1,2,3,4-tetrahydro-2-naphthylamino)- borane.

The foregoing reactions ideally lend themselves to a continuous process in which the reactants are introduced into a distillation column and alcohol or its ester-azeotrope is removed from the top of the column and tris- (alkylamino)borane is removed from the bottom.

Other modes of applying the principle of the invention may be employed, change being made as regards the details described, provided the features stated in any of the following claims or the equivalent of such be employed.

We, therefore, particularly point out and distinctly claim as our invention:

1. The method of producing tris(organoamino)boranes which comprises the reaction of one mole of a trialkyl borate ester, the alkyl group of said ester having from 1 to 5 carbons atoms, with at least three moles of a material selected from the group consisting of primary alkyl amines, the alkyl group of said amine having from 4 to a 12 carbon atoms, cyclohexylamine, cyclopentylamine, and tetrahydronaphthylamine and isolating tris(organoamino)boranes from the reaction mass.

2. The method of producing tris (n-butylamino)borane which comprises reacting methyl borate with n-butylamine in such amounts that one mole of methyl borate reacts with at least three moles of n-butylamine.

3. The method of producing tris(cyclohexylamino)- borane Which comprises reacting one mole of isopropyl borate with at least three moles of cyclohexylamine.

4. The method of producing tris(cyclopentylamino)- borane which comprises reacting one mole of isopropyl borate with at least three moles of cyclopentylamine.

5. The method of producing tris(l,2,3,4-tetrahydr0-2 naphthylamino)borane which comprises reacting one mole of n-butyl borate with at least three moles of 1,2,3,4- tetrahydrO-Z-naphthylamine.

References Cited in the file of this patent UNITED STATES PATENTS Tulleners Aug. 23, 1938 OTHER REFERENCES Couucler: Journal fiir Praktische Chemie, vol. 18, pp. 383-84 (1878).

Urs: Journal American Chemical Society, vol. 74, p. 2948 (1952).

Goubeau et al.: Zeitschrift f'tir Anorg. und allge. chem, vol. 268 pages 145-158 (1952). 

1. THE METHOD OF PRODUCING TRIS (ORGANOAMINO) BORANES WHICH COMPRISES THE REACTION OF ONE MOLE OF A TRIALKYL BORATE ESTER, THE ALKYL GROUP OF SAID ESTER HAVING FROM 1 TO 5 CARBONS ATOMS, WITH AT LEAST THREE MOLES OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF PRIMARY ALKYL AMINES, THE ALKYL GROUP OF SAID AMINE HAVING FROM 4 TO 12 CARBON ATOMS, CYCLOHEXYLAMINE, CYCLOPENTYLAMINE, AND TETRAHYDRONAPHTHYLAMINE AND ISOLATING TRIS(ORGANOAMINO) BORANES FROM THE REACTION MASS. 